1. Field of the Invention
The present invention relates to an extension/retraction device to be used for a tripod of a camera or the like, and relates more specifically to an extension/retraction device configured so that the length can be adjusted steplessly and so that the length can be maintained easily.
2. Background Art
In recent years, the change from journalizing processing in which journal entries are recorded in a ledger in detail every day to journalizing processing in which pieces of data are input by installing accounting software on personal computers has been made in daily account/tax processing jobs in business enterprises, organizations, and sole proprietors.
In general, a tripod of a camera, a stepladder or the like is configured so that the length of a leg section can be adjusted freely, and furniture such as a table or a chair is also configured so that the length of a leg section can be adjusted. As an element (which will be hereinafter referred to as an extension/retraction device) for making the length of a leg section variable, a structure for fitting a movable leg section at a lower side in or on a stationary leg section at an upper side so as to be extended and retracted freely in the longitudinal direction and affixing the position of the movable leg section using a thumbscrew or the like is known, for example. Such a structure, however, has a problem that operation of a thumbscrew takes time and therefore adjustment of the length of a leg section cannot be achieved in a short time. Therefore, a simple structure for adjusting the length of a leg section efficiently is required in recent years as solution for the above problem, and some new devices have been made regarding a simple structure.
For example, Patent Document 1 discloses a tripod named “Tripod for Surveying Machine,” which is configured so that a movable leg is supported on as to be freely slidable along the longitudinal direction with respect to a stationary leg which has an upper part supported at a tripod head section so as to be freely pivotable and so that the movable leg is affixed and held at a desired relative position with respect to the stationary leg.
The tripod in Patent Document 1 is provided with, as a device for affixing and holding the movable leg: an engagement member which runs along the longitudinal direction of the movable leg; a displacement member which is installed so as to be freely movable integrally with the movable leg and so as to be displaceable between a first state to be frictionally engaged with an engagement member and a second state to be separated from the engagement member; and a biasing member for biasing the displacement member to the first state.
Such a structure has an effect that slide movement of the movable leg is regulated when the displacement member is biased by the biasing member and frictionally engaged with the engagement member. Moreover, such a structure has an effect that slide movement of the movable leg is allowed when the displacement member is separated from the engagement member against bias force of the biasing member. Accordingly, it is possible to simply achieve extension/retraction adjustment of a leg section and easily achieve fine adjustment of the height of a tripod.
Moreover, Patent Document 2 discloses a device named “Extension/Retraction Device,” which is an extension/retraction structure of a leg section that is to be used for a tripod or the like and is configured so that the length of the leg section can be adjusted easily and so that the device can be downsized.
The device disclosed in Patent Document 2 is provided with: a leg section which is a hollow cylinder having a window section at a part thereof and which has an open end; an extension/retraction leg section which has a tip section fitted in the open end of the leg section and which can slide at the inside thereof; a spiral length adjustment member which is located in series with the extension/retraction leg section from the tip section of the extension/retraction leg section; an extension/retraction member which is held inside the leg section and which is provided from the tip section of the extension/retraction leg section and located inside or outside the length adjustment member; and an engagement member for engaging at least the length adjustment member at the window section provided at the leg section.
With such a structure, when the extension/retraction leg section slides and is inserted into the leg section, the length adjustment member slides in conjunction therewith and the extension/retraction member is retracted. In addition, when the engagement member is inserted from the window section of the leg section at the time the extension/retraction leg section slides to a desired length, the engagement member penetrates a space of the length adjustment member positioned at the window section, so that movement of the length adjustment member, the extension/retraction leg section and the extension/retraction member are inhibited. On the other hand, when the engagement member is removed from the space of the length adjustment member, bias force of the extension/retraction member, which has been retracted, automatically extends the extension/retraction leg section. Moreover, when a pulling spring formed in a spiral shape is used as the length adjustment member, a number of spaces which can be penetrated by the engagement member exist steplessly, and it is therefore possible to freely achieve length adjustment. Furthermore, it is possible to downsize the entire device, since the extension/retraction member is located inside or outside the length adjustment member.